No I'm saying that what makes sense to me is there is only physical bond when a cured finish is sanded. I'm also saying that I don't know if there actually is any chemical bond at any point, unless more coats are added to a finish not completely cured so it is still susceptible to (dissolved by) the solvents in the newly added coats.

The chemistry and science of paint finishes fascinates me, and when I work on my car, I really try to apply the science I know with the art and skills I try to learn here and elsewhere. I just wish I knew more about the actual chemistry. What I'm saying in the above paragraph are just musings...educated guesses maybe, but don't accept them as the truth. I'm not a chemist.

What else could it be if the solvents from the next application, be it paint or clear or what ever, what could it be if not a "chemical bond"? If the solvents are going into the substrate "joining" with the substrate, what else would it be called? Is there another "level" of this that WOULD be "chemical bond" but simply solvents soaking into the substrate isn't?